Preparation method of fluorine-containing ionomer composite material with ion exchange function

ABSTRACT

The present provides a method for preparing a composite material, wherein the method comprises the following steps: (1) compounding a dispersion solution of an ion exchange resin containing a free radical initiator and a high-valence metal compound, with a functional monomer-grafted porous fluoropolymer membrane with a microporous structure by performing solution pouring, tape casting, screen printing process, spraying, or impregnating process; (2) subjecting a wet membrane to heat treatment at 30˜300° C., so that the free radical initiator can initiate crosslinking reaction between the porous membrane and the resin to obtain the composite material.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 13/805,327 filed on Dec. 18, 2012, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention belongs to the field of functional polymercomposite materials, and relates to a preparation method offluorine-containing ionomer composite material with ion exchangefunction.

BACKGROUND TECHNOLOGIES

Proton Exchange Membrane Fuel Cell is a power generation device whichdirectly converts chemical energy into electrical energy in anelectrochemical manner, and is considered to be the most preferred cleanand efficient power generation technology in the 21st century. ProtonExchange Membrane (PEM) is a key material for use in Proton ExchangeMembrane Fuel Cell (PEMFC).

The perfluorosulfonic acid proton exchange membranes currently used havea good proton conductivity and chemical stability at a relatively lowtemperature (8 0° C.) and highhumidity. However, they have manyshortcomings, such as poor dimensional stability, low mechanicalstrength, bad chemical stability and so on. The membrane has differentwater absorption under different humidities, resulting in differentexpansion in size, when the membrane transforms under differentoperation conditions, the size of the membrane changes accordingly. Suchcase is repeated over and over again then mechanical damage iseventually caused to the proton exchange membrane. Moreover, a largenumber of substances with strong oxidability, such as hydroxyl radicalsand hydrogen peroxides, are produced in a reaction at the positiveelectrode of a fuel cell, and these substances will attack thenon-fluoro groups in the membrane-forming resin molecules, leading tochemical degradation, damage and blistering of the membrane. Finally,when the operating temperature of the perfluorosulfonic acid exchangemembrane is higher than 90° C., the proton conductivity of the membraneis decreased sharply due to rapid dehydration of the membrane, therebydecreasing efficiency of the fuel cell greatly. However, high operatingtemperature can greatly improve the resistance of the fuel cell catalystto carbon monoxides. In addition, the existing perfluorosulfonic acidmembranes have some hydrogen or methanol permeability, especially in adirect methanol fuel cell, permeability of methanol is very high, whichbecomes a fatal problem. Therefore, how to improve strength of aperfluorosulfonic acid proton exchange membrane, dimensional stability,and efficiency of proton conduction at a high temperature and to reducepermeability of the working medium and the like becomes a major issuethat the fuel cell industry faces.

At present, some methods have been proposed to solve these problems. Forexample, Japanese Patent No. JP-B-5-75835 enhances strength of amembrane by impregnating a porous media made of polytetrafluoroethylene(PTFE) with a perfluorosulfonic acid resin. However, this porous PTFEmedium still cannot solve the problems above due to relative softnessand insufficient reinforcing effect of the PTFE material. W. L. GoreCo., Ltd developed composite membrane liquid of Gore-Select series byfilling Nafion ion conductive liquid with the porous Teflon (U.S. Pat.No. 5,547,551, U.S. Pat. No. 5,635,041, U.S. Pat. No. 5,599,614). Thismembrane has high proton conductivity and better dimensional stability,however, Teflon has large creep at a high temperature, resulting inperformance degradation. Japanese Patent No. JP-B-7-68377 also proposesa method in which a porous media made of polyolefin is filled with aproton exchange resin, but such membrane has insufficient chemicaldurability and thus there is a problem in long-term stability.Furthermore, due to addition of the porous medium without protonconductivity, the number of proton-conduction pathways is reduced, andproton exchange capability of the membrane is decreased.

Furthermore, Japanese Patent No. JP-A-6-231779 proposes another methodfor reinforcement by using fluorine resin fibers. The membrane made bythis method is an ion exchange membrane which is reinforced through thereinforcing material of a fluorocarbon polymer in the form of fibrils.However, in this method, it is required to add a relatively large amountof the reinforcing material; in this case, processing of the membranetends to be difficult and electrical resistance of the membrane maylikely increase.

European Patent No. EP0875524B1 discloses a technology of reinforcingnafion membrane by using glassfiber membrane prepared by applying glassfiber nonwoven technology. Oxides such as silica are also mentioned inthis patent. However, non-woven glass fiber cloth is a necessarysubstrate in this patent, which would greatly limit the applicationscope of reinforcement.

U.S. Pat. No. 6,692,858 discloses a technology in which aperfluorosulfonic acid resin is reinforced by polytetrafluoroethylenefibers. In this technology, the perfluorosulfonyl fluoride resin and thepolytetrafluoroethylene fiber are mixed, extruded, and transformed toprepare a fiber-reinforced perfluorosulfonic acid resin. The methodcannot be applied in continuous production due to the time-consumingtransformation process.

CN200810638706.9 discloses a process route for preparing a crosslinkedfluorine-containing sulfonic acid proton exchange membrane by using afluorine-containing sulfonic acid resin copolymerized with a bromine- oriodine-containing perfluoromonomer under certain conditions, themembrane prepared by the method has high strength and good dimensionalstability.

However, the porous membrane or fiber is only simply mixed with a resinin the above technologies, since the nature of the membrane or fiberdiffers greatly from the membrane-forming resin, even they are mutuallyexclusive, it is extremely easy to form gaps between themembrane-forming molecules and reinforcing object, sometimes some poresof the reinforced microporous membrane cannot be filled with the resin.Thus, such a membrane often has high gas permeability, and when themembrane is working in the fuel cell, high permeability tends to resultin the energy loss and damage to the cell caused by overheating.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a composite materialwhich is formed by compounding an ion exchange resin with a porousfluoropolymer membrane, wherein the ion exchange resin and thefunctional monomers grafted on the porous fluoropolymer membrane form acarbon-chain crosslinked structure, so that the composite material hasexcellent mechanical properties and gas impermeability, as well as highion exchange capacity and electrical conductivity. Another object of thepresent invention is to provide a method for preparing said compositematerial. Yet another object of the present invention is to provide anion exchange membrane made from the above-mentioned composite material.Still another object of the present invention is to provide a fuel cellcontaining the above-mentioned ion exchange membrane. And still yetanother object of the present invention is to provide a use of theabove-mentioned composite material.

The above-mentioned objects of the present invention can be achieved byadopting the following technical schemes.

In one aspect, the present invention provides a composite material whichis formed by filling micropores and covering surface of a porousfluoropolymer membrane with one or more ion exchange resins having anion exchange function; wherein pore surfaces of the porous fluoropolymermembrane are modified by bromine-containing functional monomers throughgrafting; and at least one of the ion exchange resins forming thecomposite material can form a carbon-chain crosslinked structure withfunctional monomers grafted on the porous fluoropolymer membrane.

Preferably, said bromine-containing functional monomer is one or morecombinations selected from a group consisting of substances as definedin the following formula (V) and/or formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, and a′+b′+c′≠0; n′ is 0 or1; X₁ is selected from F or Br; and R_(f4), R_(f5), R_(f6) are selectedfrom perfluorinated alkyls, respectively.

Preferably, the ion exchange resin of said composite material isprepared by copolymerization of fluorine-containing olefins,fluorine-containing olefin monomers comprising a functional group andfluorine-containing olefin monomers containing a crosslinking siteand/or mixtures of the above-obtained copolymers, and has an EW value of600˜1,300, preferably 700˜1,200; the number average molecular weight ofsaid resin is 150,000˜450,000.

Wherein, preferably, the fluorine-containing olefin is one or moreselected from a group consisting of tetrafluoroethylene,chlorotrifluoroethylene, trifluoroethylene, hexafluoropropylene and/orvinylidene fluoride; more preferably tetrafluoroethylene and/orchlorotrifluoroethylene;

the fluorine-containing olefin monomer containing a functional group isone or more selected from a group consisting of substances as defined inthe following formula (II) and/or formula (III) and/or formula (IV):

wherein a, b, c are an integer of 0˜1, respectively, but shall not bezero at the same time;d is an integer of 0˜5; n is 0 or 1;R_(f1), R_(f2), R_(f3) are selected from perfluorinated alkyl orchlorofluorinated alkyl, respectively; X is selected from F or Br;Y₁, Y₂, Y₃ are selected from SO₂M, COOR₃ or PO(OR₄)(OR₅), respectively,wherein M is selected from F, Cl, OR, or NR₁R₂; R is selected frommethyl, ethyl or propyl, or selected from H, Na, Li, K or ammonium; R₁and R₂ are selected from H, methyl, ethyl or propyl, respectively; R₃ isselected from H, Na, Li, K, ammonium, methyl, ethyl or propyl; and R₄,R₅ are selected from H, Na, Li, K, or ammonium, respectively;the fluorine-containing olefin monomer containing a crosslinking site isone or more selected from a group consisting of substances as defined inthe following formula (V) and formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, but a′+b′+c′≠0; X₁ isselected from F or Br; n′ is 0 or 1; and R_(f4), R_(f5), R_(f6) areselected from perfluorinated alkyl, respectively.

Preferably, material of the porous fluoropolymer membrane in saidcomposite material is selected from porous polytetrafluoroethylenemembrane, polytetrafluoroethylene-hexafluoropropylene membrane, porouspolyvinylidene fluoride membrane (PVDF), porouspolytrifluorochloroethylene membrane and porouspolytetrafluoroethylene-ethylene (ETFE) membrane, which maybe uniaxialtensile membranes or biaxial tensile membranes; and the porousfluoropolymer membrane has a thickness of no greater than 100 μm, aporosity of 50˜97% and a pore size of 0.1˜10 μm; preferably, the porousfluoropolymer membrane has a thickness of 5˜20 μm, a porosity of 60˜97%,and a pore size of 0.2˜5 μm.

Preferably, said composite material may further contain a high-valencemetal compound, part of acidic exchange groups of the ion exchange resinform physical bonding in between through the high-valence metalcompound; preferably, the high-valence metal compound forming thephysical bonding is one or more combinations selected from a groupconsisting of compounds of the following elements: W, Zr, Ir, Y, Mn, Ru,Ce, V, Zn, Ti, and La; more preferably, the high-valence metal ioncompound is selected from nitrates, sulfates, carbonates, phosphates,acetates of these metal elements in the highest valence state andintermediate valence state or doulbe salts thereof; or one or moreselected from a group consisting of cyclodextrins, crown ethers,acetylacetones, aza crown ethers and nitrogen heterocyclic rings, EDTA,DMF, and DMSO complexes of these metal elements in the highest valencestate and intermediate valence state; or selected from a groupconsisting of hydroxides of these metal elements in the highest valencestate and intermediate valence state; or selected from a groupconsisting of oxides of these metal elements in the highest valencestate and intermediate valence state which have a perovskite structure,including but not limited to the following compounds: Ce_(x)Ti_((1-x))O₂(x=0.25˜0.4), Ca_(0.6)La_(0.27)TiO₃, La_((1-y))Ce_(y)MnO₃ (y=0.1˜0.4)and La_(0.7)Ce_(0.15)Ca_(0.15)MnO₃; preferably, the high-valence metalcompound is added in an amount of 0.0001˜5 wt %, preferably 0.001˜1 wt %of the resin.

In another aspect, the present invention provides a method for preparingthe above-mentioned composite material, which comprises initiating thefunctional monomers grafted on the porous membrane and bromine atoms ofthe resin by a free radical initiator to generate free radicals, andforming a carbon-chain crosslinked structure between the porous membraneand the resin through coupling between the free radicals;

wherein the initiator is one or more selected from a group consisting oforganic peroxide initiators and/or azo initiators;wherein the peroxide initiators are initiators as defined in thefollowing formula (VIII) and/or formula (IX):

R₁, R are selected from but not limited to the following groups,respectively: H, C1˜C20 alkyl or aryl-substituted alkyl, C1-C20 acyl,C1˜C20 aroyl, C1˜C20 fluorinated alkyl or perfluorinated alkyl or arylsubstituted alkyl, C1˜C20 fluorinated acyl or perfluorinated acyl,and/or C1˜C20 fluorinated aroyl or perfluorinated aroyl; but R₁ and R₂are not H at the same time;R₃, R₄ are selected from but not limited to the following groups,respectively: C1˜C20 alkyl or aryl-substituted alkyl and/or C1˜C20fluorinated alkyl or perfluorinated alkyl or aryl substituted alkyl;the azo initiator is selected from but not limited to the followinginitiators: azodicarbonamide, azobisisobutyronitrile,azobisisovaleronitrile, azobisisoheptonitrile, dimethyl2,2′-azobis(2-methylpropionate), 1-((cyano-1-methylethyl)azo) formamide,1,1′-azo(cyclohexyl-1-cyano), 2,2′-azobis(2-methylpropionamidine)dihydrochloride, and/or 4,4′-azobis(4-cyanovaleric acid);preferably, the free radical initiator is an organic peroxide initiator,and more preferably is an organic perfluorinated peroxide; for themethod of forming crosslinking, please refer to U.S. Pat. No. 3,933,767and EP1464671A1; the free radical initiator is added in an amount of0.1˜1 wt % of the resin.

Preferably, the method for preparing the composite material containing ahigh-valence metal ion compound comprises the following steps:

(1) Compounding a dispersion solution of the ion exchange resincontaining free radical initiator and high-valence metal compound withthe functional monomer-grafted porous fluoropolymer membrane with amicroporous structure by performing solution pouring, tape casting,screen printing process, spraying, or impregnating process;(2) Subjecting a wet membrane to heat treatment at 30˜300° C. so thatthe free radical initiator can initiate crosslinking reaction betweenthe porous membrane and the resin to obtain the composite material;wherein a solvent used in the processes of solution pouring, tapecasting, screen printing, spraying, impregnating and other processes, isselected from one or more of a group consisting of dimethylformamide,dimethylacetamide, methylformamide, dimethylsulfoxide,N-methylpyrrolidone, hexamethylphosphoric acid amine, acetone, water,ethanol, methanol, (n-)propanol, isopropanol, ethylene glycol and/orglycerol; preparation is performed under the following conditions:concentration of the resin dispersion solution being 1˜80%, temperatureof heat treatment being 30˜300° C., and time of heat treatment being1˜600 minutes; preferably under the following conditions: concentrationof the resin dispersion solution being 5˜40%, temperature of heattreatment being 120˜250° C., and time of heat treatment being 5˜200minutes; preferably, the initiator is added in an amount of 0.1˜1 wt %of the resin, and the high-valence metal compound is added in an amountof 0.0001˜5 wt %, preferably 0.001˜1 wt % of the resin.

In yet another aspect, the present invention provides an ion exchangemembrane made from the above-mentioned composite material.

In still another aspect, the present invention provides a fuel cellcontaining the above-mentioned ion exchange membrane.

In still yet another aspect, the present invention provides a use of theabove-mentioned composite material in manufacturing an ion exchangemembrane of a fuel cell.

Compared with the prior art, the present invention has at least thefollowing advantages:

in the composite material of the present invention, there is at leastone ion exchange resin containing bromine, and the bromine of the ionexchange resin and the bromine grafted on the porous membrane form acarbon-chain crosslinked structure. Due to formation of the carbon-chaincrosslinked structure, the composite material can form a tight integralstructure. In a preferred embodiment, a physical bond crosslinkedstructure is formed between the high-valence metal and the acidic groupin the ion exchange resin. Therefore, the ion exchange membrane madefrom the composite material of the present invention has a high ionexchange capacity, as well as good mechanical strength, gasimpermeability and stability. Compared with the ion exchange membranesmade from ordinary composite materials, the ion exchange membrane madefrom the composite material of the present invention is superior to theordinary ion exchange membranes in terms of performances such aselectrical conductivity, tensile strength, hydrogen permeation current,and dimensional change rate.

The following is detailed description of the present invention.

The perfluorosulfonic acid ion membrane used in a fuel cell needs tomeet the following requirements: being stable, having high electricalconductivity and high mechanical strength. Generally, with an increaseof ion exchange capacity, the Equivalent Weight (EW) value of theperfluoropolymer decreases (when the EW value decreases, the IonExchange Capacity (IEC)=1,000/EW) and the strength of the membrane alsodecreases in the meanwhile. Gas permeability of the membrane will alsorise accordingly, which will bring very serious effects to fuel cells.Therefore, preparing the membrane having a high ion exchange capacity,as well as good mechanical strength, gas impermeability and stability isthe key in practical applications of fuel cells, especially fuel cellsin delivery vehicles such as automobiles.

In view of the deficiencies existing in the prior art, the presentinvention provides a composite material and method for preparing thecomposite material. The composite material provided in the presentinvention uses porous membrane as a reinforcing material, which changesthe previous method of simply filling the ion exchange resin into theporous membrane structure by forming a carbon-chain crosslinkedstructure between the porous membrane and the ion exchange resin (asshown in FIG. 1) The membrane obtained has very high mechanicalproperties and gas impermeability.

The present invention provides a composite material which ischaracterized in that:

(a) Said composite material is formed by filling micropores and coveringsurfaces of a porous fluoropolymer membrane with one or more ionexchange resins having an ion exchange function;(b) The pore surfaces of said porous fluoropolymer membrane are modifiedby bromine-containing functional monomers through grafting; and(c) At least one of the ion exchange resins forming the compositematerial can form a carbon-chain crosslinked structure with thefunctional monomers grafted on the porous fluoropolymer membrane.

The selected porous fluoropolymer membrane with a microporous structuregrafted with a substance with ion exchange function has a thickness ofno greater than 100 μm, a porosity of 50˜97% and a pore size of 0.1˜10μm; preferably, the porous fluoropolymer membrane has a thickness of5˜20 μm, a porosity of 60˜97% and a pore size of 0.2˜5 μm. These porousfluoropolymer membranes are characterized in that: the material of theporous fluoropolymer membrane is selected from porouspolytetrafluoroethylene membrane,polytetrafluoroethylene-hexafluoropropylene membrane, porouspolyvinylidene fluoride membrane (PVDF), porouspolytrifluorochloroethylene membrane and porouspolytetrafluoroethylene-ethylene (ETFE) membrane. These membranes may beuniaxial tensile membranes or biaxial tensile membranes.

A graft reaction occurs between bromine-containing functional monomersand porous fluoropolymer membrane in the presence of plasma and theresulting chemical bonding crosslinked network structure is shown in thefollowing formula (I):

wherein G₁=CF₂ or O; G₂=CF₂ or O; and R_(f) is a C2-C10 perfluorinatedcarbon chain or chlorine-containing perfluorinated carbon chain.

The bromine-containing functional monomer grafted on the porous membraneis one or more selected from substances as defined in the followingformula (V) and formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, but a′+b′+c′≠0; X₁ isselected from F or Br; n′ is 0 or 1; and R_(f4), R_(f5), R_(f6) areselected from fluorine or perfluorinated alkyl, respectively.

The method for modifying the porous membrane with the above-mentionedmonomer is a plasma method, which has been disclosed in manypublications, specifically, please refer to polyvinylidene fluoride(PVDF) nanofiber modified and grafted by plasma as disclosed in Page 33,Journal of Tianjin Polytechnic University, 2008, Vol. 27, Iss. 5.

Said fluorine-containing ion exchange resin of the present invention isprepared by copolymerization of fluorine-containing olefins, one or morefluorine-containing olefin monomers comprising a functional group andone or more fluorine-containing olefin monomers containing acrosslinking site, or mixtures of the above-obtained copolymers, thefluorine-containing ion exchange resin has a EW value of 600˜4,300,preferably 700˜1,200, and a number average molecular weight of150,000˜450,000.

The fluorine-containing olefin is one or more selected from a groupconsisting of tetrafluoroethylene, chlorotrifluoroethylene,trifluoroethylene, hexafluoropropylene and/or vinylidene fluoride;preferably selected from tetrafluoroethylene and/orchlorotrifluoroethylene.

The fluorine-containing olefin monomer containing a functional group isone or more selected from a group consisting of monomers as defined inthe following formula (II), formula (III) and formula (IV):

wherein a, b, c are an integer of 0˜1, respectively, but shall not bezero at the same time;d is an integer of 0˜5;n is 0 or 1;R_(f1), R_(f2), R_(f3) are selected from perfluorinated alkyl orchlorofluorinated alkyl, respectively;X is selected from F or Br;Y₁, Y₂, Y₃ are selected from SO₂M, COOR₃ or PO(OR₄)(OR₅), respectively,wherein M is selected from F, Cl, OR, or NR₁R₂; R is selected frommethyl, ethyl or propyl, or selected from H, Na, Li, K or ammonium; R₁and R₂ are selected from H, methyl, ethyl or propyl, respectively; R₃ isselected from H, Na, Li, K, ammonium, methyl, ethyl or propyl; R4, R5are selected from H, Na, Li, K, or ammonium, respectively.

The fluorine-containing olefin monomer containing a crosslinking site isone or more selected from a group consisting of monomers as defined inthe following formula (V) and/or formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, but a′+b′+c′≠0;X₁ is selected from F or Br;n′ is 0 or 1; andR_(f4), R_(f5), R_(f6) are selected from fluorine or perfluorinatedalkyls, respectively.

Said carbon chain crosslinking means forming a carbon-carbon bondbetween the functional monomer grafted on the porous fluoropolymermembrane and the ion exchange resin, which are crosslinked together (asshown in FIG. 2).

The method for forming carbon-chain crosslinking between the porousmembrane and the membrane-forming resin comprises initiating thefunctional monomers grafted on the porous membrane and bromine atoms ofthe resin by a free radical initiator to generate free radicals, thenobtaining crosslinked carbon-carbon bonds through coupling between thefree radicals; wherein the initiators used include organic peroxideinitiators and azo initiators; preferably, the initiator is an organicperoxide initiator; more preferably, the initiator is a perfluorinatedorganic peroxide initiator.

Said free radical initiators are organic peroxide initiators or azoinitiators, or two or more of the free radical initiators to be usedsynergistically; wherein the peroxide initiators are initiators asdefined in the following formula (VIII) and formula (IX):

R₁, R₂ are selected from but not limited to the following groups,respectively: H, C1˜C20 alkyl or aryl-substituted alkyl, C1˜C20 acyl,C1˜0 aroyl, C1˜C20 fluorinated alkyl or perfluorinated alkyl or arylsubstituted alkyl, C1˜C20 fluorinated acyl or perfluorinated acyl,and/or C1˜C20 fluorinated aroyl or perfluorinated aroyl; but R₁ and R₂are not H at the same time;R₃, R₄ are selected from but not limited to the following groups,respectively: C1˜C20 alkyl or aryl-substituted alkyl and/or C1˜C20fluorinated alkyl or perfluorinated alkyl or aryl substituted alkyl;the azo initiator is selected from but not limited to the followinginitiators: azodicarbonamide, azobisisobutyronitrile,azobisisovaleronitrile, azobisisoheptonitrile, dimethyl2,2′-azobis(2-methylpropionate), 1-((cyano-1-methylethyl)azo) formamide,1,1′-azo(cyclohexyl-1-cyano), 2,2′-azobis(2-methylpropionamidine)dihydrochloride, and/or 4,4′-azobis(4-cyanovaleric acid).

In the present invention, a high-valence metal compound is added to thecomposite material so that part of acidic exchange groups of the ionexchange resin can form physical bonding in between through thehigh-valence metal compound.

Said high-valence metal compound forming the physical bonding is one ormore combinations selected from a group consisting of compounds of thefollowing elements: W, Zr, Ir, Y, Mn, Ru, Ce, V, Zn, Ti, and La;

Said high-valence metal ion compound is one or more selected from agroup consisting of nitrates, sulfates, carbonates, phosphates, acetatesof these metal elements in the highest valence state and intermediatevalence state or double salts thereof Said high-valence metal ioncompound is or selected from a group consisting of cyclodextrins, crownethers, acetylacetones, aza crown ethers and nitrogen heterocyclicrings, EDTA, DMF, and DMSO complexes of these metal elements in thehighest valence state and intermediate valence state. Said high-valencemetal ion compound is selected from a group consisting of hydroxides ofthese metal elements in the highest valence state and intermediatevalence state. Said high-valence metal ion compound is selected from agroup consisting of oxides of these metal elements in the highestvalence state and intermediate valence state which have a perovskitestructure, including but not limited to the following compounds:Ce_(x)Ti_((1-x))O₂ (x=0.25˜0.4), Ca_(0.6)La_(0.27)TiO₃,La_((1-y))Ce_(y)MnO₃ (y=0.1˜0.4) and La_(0.7)Ce_(0.15)Ca_(0.15)MnO₃. Thehigh-valence metal compound is added in an amount of 0.0001˜5 wt %,preferably 0.001˜1 wt %.

The method for preparing said composite material containing ahigh-valence metal compound includes the following steps:

(1) Compounding a dispersion solution of the ion exchange resincontaining free radical initiator and high-valence metal compound withthe functional monomer-grafted porous fluoropolymer membrane with amicroporous structure by performing solution pouring, tape casting,screen printing process, spraying, or impregnating process;(2) Subjecting a wet membrane to heat treatment at 30˜250° C. so thatthe free radical initiator can initiate crosslinking reaction betweenthe porous membrane and the resin;(3) Obtaining the composite material after treatment.

The solvent used in the processes of solution pouring, tape casting,screen printing, spraying, impregnating and other processes, is selectedfrom one or more of a group consisting of dimethylformamide,dimethylacetamide, methylformamide, dimethylsulfoxide,N-methylpyrrolidone, hexamethylphosphoric acid amine, acetone, water,ethanol, methanol, (n-)propanol, isopropanol, ethylene glycol and/orglycerol; concentration of the resin solution used is 1˜80%, preferably5˜40%; temperature of heat treatment is 30˜300° C., preferably 120˜250°C.; and time of heat treatment is 1˜600 minutes, preferably 5˜200minutes.

In another aspect, the present invention provides an ion exchangemembrane made from the above-mentioned composite material.

In yet another aspect, the present invention provides a fuel cellcontaining the above-mentioned ion exchange membrane.

In still another aspect, the present invention provides a use of theabove-mentioned composite material in manufacturing an ion exchangemembrane of a fuel cell.

The beneficial effects of the present invention include:

The present invention provides an ion exchange composite material withreinforced porous membrane where a chemical crosslinked structure isformed between the composite base porous membrane and themembrane-forming resin through chemical bonds; in a preferredembodiment, part of the acidic exchange groups in the ion exchange resinform a physical bonding crosslinked network through high-valence metalphysical bonding. Since the porous membrane is grafted with functionalgroups with exchange function, the porous membrane and the ion exchangeresin can form a tight integral structure through chemical crosslinking,rather than simply blending ion exchange resin and microporous membranetogether in the prior art. The composite material obtained in thepresent invention has advantages of excellent chemical stability,mechanical properties and gas permeability etc, and the ion exchangemembrane provided in the present invention resolves the problems thatthe conventional microporous composite membrane has poor gasimpermeability and the ion exchange resin is easily separated from themicroporous membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an ion exchange resin with carbon-chain crosslinked on aporous membrane.

FIG. 2 shows a schematic diagram illustrating carbon-chain crosslinking;

wherein “1” represents a perfluorinated ion exchange resin, “2”represents a porous membrane, “3” represents a molecule ofperfluorinated ion exchange resin, and “4” represents chemicalcrosslinking.

FIG. 3 shows a polarization curve of a single cell.

BEST MODES OF THE PRESENT INVENTION

The present invention will be further illustrated in combination withembodiments, which are not used to limit the present invention.

Example 1

A chqistex polytetrafluoroethylene membrane (bought in Ningbo, China)with a thickness of 18 μm, a porosity of 85% and a pore size of 1 μm wasplaced in a plasma generator and a plasma generated at a pressure of 1Pa with Ar as working gas was grafted with the monomer defined in thefollowing formula

(wherein e=1).

The grafted polytetrafluoroethylene membrane was impregnated in anethanol-water solution containing 5% cerium (III) nitrate, a trace of2,2′-azobis-(2-methylbutyronitrile) and 25% perfluorosulfonic acid resinfor 10 minutes (wherein the structural formula of the perfluorosulfonicacid resin is shown in the following formula:

number average molecular weight: 170,000). Then the wet membrane wastaken out, and treated at 190° C. for 20 minutes to obtain a compositemembrane with a thickness of 19 μm.

Example 2

A (n-)propanol-water mixed solution containing a solution of 15% mixedperfluorosulfonic acid resin, wherein resin A comprising a repeatingunit (a):

(number average molecular weight: 260,000) and resin B comprising arepeating unit (b):

(number-average molecular weight: 170,000) (the mass ratio of the resinA to resin B is 3:1), 3% manganese (II) nitrate and a trace of benzoylperoxide, was sprayed onto a chqistex polytetrafluoroethylene membrane(bought in Ningbo) with a thickness of 10 μm, a porosity of 80% and apore size of 0.5 μm which was grafted with a monomer:

(wherein e=2) according to the graft method in Example 1

Then a sample of the wet membrane was dried at 140° C. for 15 minutes inan oven. In order to block the pores in the membrane completely, thisstep may be repeated for more than two times. Finally, the compositemembrane was treated at 150° C. for 30 minutes to obtain a compositemembrane with a thickness of 20 μm.

Example 3

An isopropanol-(n-)propanol-water solution with a mass concentration of10% was prepared by mixing a perfluorosulfonic acid resin A comprising arepeating unit (a):

(number average molecular weight: 260,000) and a perfluorosulfonic acidresin B comprising a repeating unit (b):

(number average molecular weight: 170,000) (the mass ratio of the resinA to resin B is 5:1); the isopropanol-(n-)propanol-water solutionfurther contained La (III)-DMF complex and a trace of perfluorinateddilauroyl peroxide

Then a chqistex polytetrafluoroethylene membrane (bought in Ningbo) witha thickness of 10 μm, a porosity of 90% and a pore size of 2˜3 μmgrafted with

(wherein e=1) according to the graft method in Example 1 was compoundedwith the above-mentioned isopropanol-(n-)propanol-water solution byfollowing the screen printing method, and the membrane obtained wastreated at 180° C. for 5 minutes to obtain a membrane with a thicknessof 11 μm.

Example 4

A polyvinylidene fluoride membrane with a thickness of 30 μm, a porosityof 79% and a pore size of 0.22 μm which was grafted with both

(wherein e=1)and

(wherein e=0)(mass ratio of the two monomers is 1:1) (produced by Zhejiang (Torch)Xidoumen Membrane Industry Co., Ltd, according to the grafting method inExample 1)was impregnated in the DMF solution containing 10% zirconium nitrate, atrace of perfluorinated malonyl peroxide and 5% perfluorosulfonic acidresin, wherein the perfluorosulfonic acid resin has a structural formulaformulas:

(number average molecular weight: 170,000). Then a sample of the wetmembrane was dried at 100° C. for 40 minutes in an oven and then treatedat 190° C. for 20 minutes to obtain a composite membrane with athickness of 31 μm.

Example 5

A chqistex polytetrafluoroethylene membrane (bought in Ningbo) with athickness of 50 μm, a porosity of 95% and a pore size of 0.5 μm whichwas grafted with both

(wherein e=0)and

(wherein e=1) (mass ratio of the two monomers is 1:1) according to thegrafting method in Example 1 was fixed by a tensioning device around themembrane.

A DMSO solution containing 4% zinc-cyclodextrin complex, a trace ofperfluorinated malonyl peroxide and 30% perfluorosulfonic acid resin wassprayed onto both sides of the polytetrafluoroethylene membrane, whereinthe perfluorosulfonic acid resin has a structural formula as:

(a=9; b=6; c=3; a′=b′=c′=1; n=1; x=10, y=12, z=1; number averagemolecular weight: 170,000).

Then a sample of the wet membrane was dried at 160° C. for 10 minutes inan oven. In order to block the pores in the membrane completely, thisstep may be repeated for more than two times. Finally, the compositemembrane was treated at 200° C. for 20 minutes to obtain a compositemembrane with a thickness of 50 μm.

Example 6

A porous polyvinylidene fluoride membrane with a thickness of 25 μm, aporosity of 70% and a pore size of 1 μm grafted with twobromine-containing monomers that are the same as those in Example 5(mass ratio of the two monomers is 2.5:1) according to the graftingmethod in Example 1 was fixed on a plate after treatment with thesolution. And a (n-)propanol-water solution containing 0.01% ceriumnitrate, a trace of perfluorinated malonyl peroxide and 20% mixedperfluorosulfonic acid resins, wherein the perfluorosulfonic acid resinA comprises a repeating unit (a)

(number average molecular weight: 290,000) and the perfluorosulfonicacid resin B comprises a repeating unit (b):

(a=11, b=7, c=5; a′=b′=c′=1; n=1, x=13, y=10, z=1; number averagemolecular weight: 160,000) (mass ratio of the resin A to resin B is 4:1)was sprayed onto the fixed porous polytrifluorochloroethylene membrane,A sample of the wet membrane was dried at 80° C. for 10 minutes in anoven, then the ion exchange resin contacting the porous polyvinylidenefluoride membrane was pressed into pores of the membrane through the hotpressing process to prepare a composite membrane.

Example 7

A chqistex polytetrafluoroethylene membrane (bought in Ningbo) with athickness of 10 μm, a porosity of 80% and a pore size of 1 μm which wasgrafted with both

(wherein e=0)and

(mass ratio of the two monomers is 1:3) according to the grafting methodin Example 1 was fixed by a tensioning device around the membrane. Thenan NMP solution containing 5% vanadium sulfate, a trace ofperfluorinated malonyl peroxide and 30% mixed perfluorosulfonic acidresins, wherein the perfluorosulfonic acid resin A comprises a repeatingunit (a):

(c=7, d=5, c′=d′=1; number average molecular weight: 260,000)and the perfluorosulfonic acid resin B comprises a repeating unit (b):

(number average molecular weight: 160,000) (mass ratio A:B=1:2) wastape-cast on the taut surface of the porous membrane and the solvent wasremoved by briefly heating a blower. Then the other side of the porousmembrane was coated with an ethanol-water solution of 14%perfluorosulfonic acid resin, wherein the perfluorosulfonic acid resinhas a structural formula as:

(number average molecular weight: 250,000). The ethanol-water solutionwas allowed to completely penetrate into the pores of thepolytetrafluoroethylene membrane to reach the continuous resin layer atthe first surface directly, and then a sample of the wet membrane wasdried at 150° C. for 20 minutes in an oven to obtain a compositemembrane.

Example 8

The first surface of a chqistex polytetrafluoroethylene membrane (boughtin Ningbo) with a thickness of 80 μm, a porosity of 75% and a pore sizeof 4 μm which was grafted with

according to the grafting method in Example 1 was coated with amethanol-water solution containing 0.01% manganese sulfate, a trace ofperfluorinated malonyl peroxide and 10% mixed perfluorosulfonic acidresin, wherein the mixed perfluorosulfonic acid resin was prepared bymixing the two resins below at a mass ratio of A:B=2:1, where the resinA comprises a repeating unit (a):

(number average molecular weight: 160,000) and the resin B comprises arepeating unit formula (b):

(number average molecular weight of 250,000) at a mass ratio of 3:1,

Then the solvent was removed from the wetted polytetrafluoroethylenemembrane by briefly heating a blower. In order to form a continuouslayer of the ion exchange resin on the surface of thepolytetrafluoroethylene membrane, this process were required to berepeated for more than two times. The membrane was then heated at 150°C. for 2 minutes to obtain a composite membrane.

Example 9

A polytetrafluoroethylene membrane with a thickness of 18 μm, a porosityof 80%, and a pore size of 0.5˜3 μm which was grafted with

according to the grafting method in Example 1 was tiled on a plate.

Then a DMF solution containing 20% mixed perfluorosulfonic acid resins,wherein the perfluorosulfonic acid resin A comprises a repeating unit(a):

(number average molecular weight: 160,000) and the resin B comprises arepeating unit (b),

(f=10, g=5, h=3, f′=g′=h′=1, i=0, M, M′=H, number average molecularweight: 210,000) (mass ratio of the resin A to resin B is 1:1), 0.02%cerium-18-crown-6 complex and a trace of perfluorinated malonylperoxide, was tape-cast on the above-mentioned modifiedpolytetrafluoroethylene membrane to perform lamination.

Then the laminated membrane was dried at 240° C. for 2 minutes in anoven to obtain a composite membrane.

Example 10

A propanol-water solution containing 0.03% bipyridine-Ru complex, atrace of perfluorinated malonyl peroxide and 15% perfluorinated sulfonicacid resin comprising a repeating unit as:

(number average molecular weight: 250,000) was sprayed onto apolytetrafluoroethylene membrane with a thickness of 10 μm, a porosityof 85% and a pore size of 0.5 μm which was grafted with

according to the grafting method in Example 1.

Then a sample of the wet membrane was dried at 140° C. for 30 seconds inan oven. In order to block the pores in the membrane completely, thisstep may be repeated for more than two times. Finally, the compositemembrane was processed at 150° C. for 30 minutes to obtain a membranewith a thickness of 20 μm.

Example 11

A (n-)propanol-water solution containing 15% mixed perfluorosulfonicacid resins prepared by mixing resin A comprising a repeating unit (a):

(number average molecular weight: 260,000) and resin B comprising arepeating unit (b):

(number average molecular weight: 170,000) and a trace of benzoylperoxide was sprayed onto a chqistex polytetrafluoroethylene membrane(bought in Ningbo) with a thickness of 10 μm, a porosity of 80% and apore size of 0.5 μm which was grafted with

(wherein e=1) according to the grafting method in Example 1.

Then a sample of the wet membrane was dried at 140° C. for 15 minutes inan oven. In order to block the pores in the membrane completely, thisstep may be repeated for more than two times. Finally, the compositemembrane was treated at 150° C. for 30 minutes to obtain a membrane witha thickness of 20 μm.

Example 12

An isopropanol-(n-)propanol-water solution containing 15%perfluorosulfonic acid resin, the structural formula as

(x is about 5, n=0, p=4, exchange capacity: 1.18 mmol/g; molecularweight: 230,000), was prepared.

Then a tetrafluoroethylene membrane with a thickness of 20 μM, aporosity of 90% and a pore size of 2˜3 μm was adopted to obtain amembrane with a thickness of 20 μm according to the screen printingmethod by using the above-mentioned isopropanol-(n-)propanol-watersolution.

Example 13 Preparation and Characterization of Fuel Cell MembraneElectrode Assembly

Preparation of Gas Diffusion Layer (GDL):

Torry090 carbon paper was impregnated in a 25% PTFE emulsion for anappropriate period of time, followed by hydrophobic treatment. Theamount of the impregnated PTFE was determined by weighing method. Thenthe carbon paper impregnated with PTFE was placed in a muffle furnaceand roasted at 340° C. so as to remove the surfactant in the PTFEemulsion impregnated in the carbon paper and also make the PTFEthermally melted and sintered and dispersed uniformly on the fibers ofthe carbon paper, and thereby to achieve a good hydrophobic effect. Themass fraction of PTFE in the roasted carbon paper was about 30%. Acertain amount of carbon powder, PTFE, and an appropriate amount ofisopropanol aqueous solution were mixed, oscillated with ultrasonic wavefor 15 minutes, and then coated onto the carbon papers by adopting brushcoating process, and the coated carbon papers were roasted at 340° C.for 30 minutes, respectively, to prepare a gas diffusion layer.

Preparation of Membrane Electrode Assembly (MEA):

the amount of Pt loaded in the catalyst layer was 0.4 mg/cm²; a certainamount of 40% Pt/C (JM Company) electrocatalyst, deionized water andisopropanol were mixed, oscillated with ultrasonic wave for 15 minutes;after adding a certain amount of 5% resin solution of Example 12,ultrasonic oscillation was proceeded for another 15 minutes; after thesolution turned ito an ink-like solution through ultrasonic processing,the mixed solution was sprayed onto the membrane of Example 2 uniformlyto obtain an Membrane Electrode Assembly (MEA).

The prepared membrane electrode assembly and the leveled gas diffusionlayer were combined to assemble a single cell, and galvanostaticpolarization performance test was performed in a self-designeddual-channel low-power testing platform under test conditions asfollows: effective active area of a single cell was 50 cm², pressures ofH₂ and air were both 1.0 bar, H₂ utilization rate was 70%; airutilization rate was 40%; relative humidity was 50%; and cell operatingtemperature was (95° C. The polarization curve test was performed afterthe prepared electrode was activated, and the data were recorded at aninterval of 1 minute after the respective measuring points werestabilized for 2 minutes so as to draw a polarization curve (FIG. 3).

Example 14

This example is used to illustrate respective performances of thecomposite membranes prepared in Examples 1-12.

The performances of all the membranes were characterized and the resultsare shown in Table 1. It can be seen from Table 1 that the electricalconductivity at 95° C., tensile strength, hydrogen permeation current,dimensional change rate, and other performances of the compositemembrane of the present invention are all superior to those of anordinary composite ion membrane. The test conditions of the electricalconductivity value are as follows: T=95° C., under saturated humidity;and T=25° C., dried in a drier for two days; the method for testing thetensile strength was a GB standard method (GB/T20042.3-2009), and themethod for testing the hydrogen permeation current was anelectrochemical method (Electrochemical and Solid-State Letters, 10, 5,B101-B104 2007)

TABLE 1 Characteristics of various membranes Testing Condition Nos. andMethod Results Electrical Membrane of Example 11 T = 95° C., under0.0276/0.0131 Conductivity Membrane of Example 12 saturated humidity/0.0216/0.0041 (S/cm) Membrane of Example 1 T = 25° C., dried in a0.0285/0.0109 Membrane of Example 2 drier for two days 0.0277/0.0133Membrane of Example 3 0.0296/0.0114 Membrane of Example 4 0.0289/0.0116Membrane of Example 5 0.0302/0.0121 Membrane of Example 6 0.0311/0.0131Membrane of Example 7 0.0312/0.0121 Membrane of Example 8 0.0321/0.0141Membrane of Example 9 0.0331/0.0131 Membrane of Example 10 0.0331/0.0131Tensile Membrane of Example 11 GB standard method 32 Strength Membraneof Example 12 (GB/T20042.3-2009) 28 (MPa) Membrane of Example 1 35Membrane of Example 2 33 Membrane of Example 3 34 Membrane of Example 435 Membrane of Example 5 36 Membrane of Example 6 38 Membrane of Example7 37 Membrane of Example 8 35 Membrane of Example 9 34 Membrane ofExample 10 39 Hydrogen Membrane of Example 11 Electrochemical 1.8Permeation Membrane of Example 12 method >4 Current Membrane of Example1 0.12 (mA/cm²) Membrane of Example 2 0.12 Membrane of Example 3 0.09Membrane of Example 4 0.11 Membrane of Example 5 0.11 Membrane ofExample 6 0.10 Membrane of Example 7 0.07 Membrane of Example 8 0.09Membrane of Example 9 0.06 Membrane of Example 10 0.12 DimensionalMembrane of Example 11 (GB/T20042.3-2009) 3.5 Change Rate Membrane ofExample 12 8.9 (%) Membrane of Example 1 1.0 Membrane of Example 2 1.2Membrane of Example 3 0.9 Membrane of Example 4 1.2 Membrane of Example5 1.2 Membrane of Example 6 2.1 Membrane of Example 7 1.2 Membrane ofExample 8 1.0 Membrane of Example 9 1.3 Membrane of Example 10 1.2

1. A method for preparing a composite material, the method comprising:(1) compounding a dispersion solution of an ion exchange resincontaining a free radical initiator and a high-valence metal compound,with a functional monomer-grafted porous fluoropolymer membrane with amicroporous structure by performing solution pouring, tape casting,screen printing process, spraying, or impregnating process; (2)subjecting a wet membrane to heat treatment at 30˜300° C., so that thefree radical initiator can initiate crosslinking reaction between theporous membrane and the resin to obtain the composite material; whereina solvent used in the processes of solution pouring, tape casting,screen printing, spraying, impregnating and other processes, is selectedfrom one or more of a group consisting of dimethylformamide,dimethylacetamide, methylformamide, dimethylsulfoxide,N-methylpyrrolidone, hexamethylphosphoric acid amine, acetone, water,ethanol, methanol, (n-)propanol, isopropanol, ethylene glycol and/orglycerol; preparation is performed under the following conditions:concentration of the resin dispersion solution being 1˜80%, temperatureof heat treatment being 30˜300° C., and time of heat treatment being1˜600 minutes; the acidic crosslinking catalyst is added in an amount of0.1˜1 wt % of the resin.
 2. The method for preparing a compositematerial according to claim 1, wherein the free radical initiator is oneor more selected from a group consisting of organic peroxide initiatorsand/or azo initiators.
 3. The method for preparing a composite materialaccording to claim 2, wherein the organic peroxide initiator is theinitiator as defined in the following formula (VIII) and/or formula(IX):

R₁, R₂ are selected from but not limited to the following groups,respectively: H, C₁˜C₂₀ alkyl or aryl-substituted alkyl, C₁˜C₂₀ acyl,C₁˜C₂0 aroyl, C₁˜C₂₀ fluorinated alkyl or perfluorinated alkyl or arylsubstituted alkyl, C₁˜C₂₀ fluorinated acyl or perfluorinated acyl,and/or C₁˜C₂₀ fluorinated aroyl or perfluorinated aroyl; but R₁ and R₂are not H at the same time; R₃, R₄ are selected from but not limited tothe following groups, respectively: C₁˜C₂₀ alkyl or aryl-substitutedalkyl and/or C₁˜C₂₀ fluorinated alkyl or perfluorinated alkyl or arylsubstituted alkyl.
 4. The method for preparing a composite materialaccording to claim 2, wherein the organic peroxide initiator is anorganic perfluorinated peroxide.
 5. The method for preparing a compositematerial according to claim 2, wherein the azo initiator is selectedfrom but not limited to the following initiators: azodicarbonamide,azobisisobutyronitrile, azobisisovaleronitrile, azobisisoheptonitrile,dimethyl 2,2′-azobis(2-methylpropionate), 1-((cyano-1-methylethyl)azo)formamide, 1,1′-azo(cyclohexyl-1-cyano),2,2′-azobis(2-methylpropionamidine) dihydrochloride, and/or4,4′-azobis(4-cyanovaleric acid).
 6. The method for preparing acomposite material according to claim 1, wherein the high-valence metalcompound is one or more selected from a group consisting of compounds ofthe following elements: W, Zr, Ir, Y, Mn, Ru, Ce, V, Zn, Ti, and La. 7.The method for preparing a composite material according to claim 1,wherein the high-valence metal compound is selected from nitrates,sulfates, carbonates, phosphates, acetates of these metal elements inthe highest valence state and intermediate valence state or double saltsthereof; or one or more selected from a group consisting ofcyclodextrins, crown ethers, acetylacetones, aza crown ethers andnitrogen heterocyclic rings, EDTA, DMF, and DMSO complexes of thesemetal elements in the highest valence state and intermediate valencestate; or one or more selected from a group consisting of hydroxides ofthese metal elements in the highest valence state and intermediatevalence state; or selected from a group consisting of oxides of thesemetal elements in the highest valence state and intermediate valencestate which have a perovskite structure, including but not limited tothe following compounds: Ce_(x)Ti_((1-x))O₂ (x=0.25˜0.4),Ca_(0.6)La_(0.27)TiO₃, La_((1-y))Ce_(y)MnO₃ (y=0.1˜0.4) andLa_(0.7)Ce_(0.15)Ca_(0.15)MnO₃.
 8. The method for preparing a compositematerial according to claim 1, wherein part of acidic exchange groups ofthe ion exchange resin form physical bonding in between through thehigh-valence metal compound.
 9. The method for preparing a compositematerial according to claim 1, the ion exchange resin is prepared bycopolymerization of fluorine-containing olefins, fluorine-containingolefin monomers comprising a functional group and fluorine-containingolefin monomers containing a crosslinking site and/or mixtures of theabove-obtained copolymers, and has an EW value of 600˜1,300, preferably700˜1,200; the number average molecular weight of said resin is150,000˜450,000; wherein the fluorine-containing olefin monomercontaining a functional group is one or more selected from a groupconsisting of substances as defined in the following formula (II) and/orformula (III) and/or formula (IV):

wherein a, b, c are an integer of 0˜1, respectively, but shall not bezero at the same time; d is an integer of 0˜5; n is 0 or 1; R_(f1),R_(f2), R_(f3) are selected from perfluorinated alkyl orchlorofluorinated alkyl, respectively; X is selected from F or Br; Y₁,Y₂, Y₃ are selected from SO₂M, COOR₃ or PO(OR₄)(OR₅), respectively,wherein M is selected from F, Cl, OR, or NR₁R₂; R is selected frommethyl, ethyl or propyl, or selected from H, Na, Li, K or ammonium; R₁and R₂ are selected from H, methyl, ethyl or propyl, respectively; R₃ isselected from H, Na, Li, K, ammonium, methyl, ethyl or propyl; and R₄,R₅ are selected from H, Na, Li, K, or ammonium, respectively; thefluorine-containing olefin monomer containing a crosslinking site is oneor more selected from a group consisting of substances as defined in thefollowing formula (V) and formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, but a′+b′+c′≠0; X₁ isselected from F or Br; n′ is 0 or 1; and R_(f4), R_(f5), R_(f6) areselected from perfluorinated alkyl, respectively.
 10. The method forpreparing a composite material according to claim 9, wherein thefluorine-containing olefin is one or more selected from a groupconsisting of tetrafluoroethylene, chlorotrifluoroethylene,trifluoroethylene, hexafluoropropylene and/or vinylidene fluoride. 11.The method for preparing a composite material according to claim 9,wherein said fluorine-containing olefin is tetrafluoroethylene and/orchlorotrifluoroethylene.
 12. The method for preparing a compositematerial according to claim 1, wherein the porous fluoropolymer membraneis selected from porous polytetrafluoroethylene membrane,polytetrafluoroethylene-hexafluoropropylene membrane, porouspolyvinylidene fluoride membrane (PVDF), porouspolytrifluorochloroethylene membrane and porouspolytetrafluoroethylene-ethylene (ETFE) membrane, which are uniaxialtensile membranes or biaxial tensile membranes.
 13. The method forpreparing a composite material according to claim 12, wherein the porousfluoropolymer membrane has a thickness of no greater than 100 μm, aporosity of 50˜97% and a pore size of 0.1˜10 μm.
 14. The method forpreparing a composite material according to claim 13, wherein the porousfluoropolymer membrane has a thickness of 5˜20 μm, a porosity of 60˜97%,and a pore size of 0.2˜5 μm.
 15. The method for preparing a compositematerial according to claim 1, wherein the functional monomers arebromine-containing functional monomers.
 16. The method for preparing acomposite material according to claim 15, wherein the bromine-containingfunctional monomers are selected one or more combinations fromsubstances as defined in the following formula (V) and/or formula (VI):

wherein a′, b′, c′ are 0 or 1, respectively, but a′+b′+c′≠0; n′ is 0 or1; X₁ is selected from F or Br; and R_(f4), R_(f5), R_(f6) are selectedfrom fluorine or perfluorinated alkyl, respectively.
 17. The method forpreparing the composite material according to claim 1, wherein thepreparation is performed under the following conditions: concentrationof the resin dispersion solution being 5˜40%, temperature of heattreatment being 120˜250° C., and time of heat treatment being 5˜200minutes.
 18. The method for preparing the composite material accordingto claim 1, wherein the high-valence metal compound is added in anamount of 0.0001˜5 wt % of the resin.
 19. The method for preparing thecomposite material according to claim 1, wherein the high-valence metalcompound is added 0.001˜1 wt % of the resin.
 20. A composite materialprepared by the method according to claim 1 and an ion exchange membranecomprising the composite material and a fuel cell comprising the ionexchange membrane.